Fixup under-aligned buffers for AltiVec and Power8

This commit supports the upcoming AltiVec and Power8 processor support. The commit favors AlignedSecByteBlock over SecByteBlock in places where messages are handled on the AltiVec and Power8 processor data paths. The data paths include all block cipher modes of operation, and some filters like

Intel and ARM processors are tolerant of under-aligned buffers when using crypto intstructions. AltiVec and Power8 are less tolerant, and they simply ignore the three low-order bits to ensure an address is aligned. The AltiVec and Power8 have caused a fair number of wild writes on the stack and in the heap.

Testing on a 64-bit Intel Skylake show a marked improvement in performance. We suspect GCC is generating better code since it knows the alignment of the pointers, and does not have to emit fixup code for under-aligned and mis-aligned data. Here are some data points:

  SecByteBlock
    - Poly1305: 3.4 cpb
    - Blake2s: 6.7 cpb
    - Blake2b: 4.5 cpb
    - SipHash-2-4: 3.1 cpb
    - SipHash-4-8: 3.5 cpb
    - ChaCha20: 7.4 cpb
    - ChaCha12: 4.6 cpb
    - ChaCha8: 3.5 cpb

  AlignedSecByteBlock
    - Poly1305: 2.9 cpb
    - Blake2s: 5.5. cpb
    - Blake2b: 3.9 cpb
    - SipHash-2-4: 1.9 cpb
    - SipHash-4-8: 3.3 cpb
    - ChaCha20: 6.0 cpb
    - ChaCha12: 4.0 cpb
    - ChaCha8: 2.9 cpb

Testing on an mid-2000's 32-bit VIA C7-D with SSE2+SSSE3 showed no improvement, and no performance was lost.

1 files changed, 2 insertions, 2 deletions

diff --git a/filters.h b/filters.h
index 2e56f122..6619a335 100644
--- a/filters.h
+++ b/filters.h
@@ -210,7 +210,7 @@ struct CRYPTOPP_DLL FilterPutSpaceHelper
 		{return HelpCreatePutSpace(target, channel, minSize, minSize, bufferSize);}

 

 	//! \brief Temporay working space

-	SecByteBlock m_tempSpace;

+	AlignedSecByteBlock m_tempSpace;

 };

 

 //! \class MeterFilter

@@ -414,7 +414,7 @@ protected:
 		size_t MaxSize() const {return m_buffer.size();}

 

 	private:

-		SecByteBlock m_buffer;

+		AlignedSecByteBlock m_buffer;

 		size_t m_blockSize, m_maxBlocks, m_size;

 		byte *m_begin;

 	};